(1) Field of the Invention
This invention generally relates to a broadband, towed line array with spatial discrimination capabilities. More particularly, this invention relates to towed line array technology that relies on simple monopole sensors typically operating in a receive mode only and utilizing a novel modular sub-array arrangement.
(2) Description of the Prior Art
Several underwater sonar applications exist for steered directional acoustic beams. Although the current towed systems provide spatial discrimination in the direction of tow, a left right ambiguity exists due to the omni-directional sensors employed. Given the orientation of the array in revolution, a directional sensor would resolve this ambiguity and provide essentially three-dimensional spatial discrimination.
Typical sensors used in today's towed line arrays consist of solid piezoceramic spheres or cylinders. However, in some special cases they consist of fiber optic cables wound onto mandrels or miniature flextensional transducers. In any case, the element dimensions are small compared to the acoustic wavelength, and thus these sensors operate below their first mechanical resonance.
The following patents, for example, disclose towed arrays, but do not disclose a modular sub-array such as that taught in the curent invention which may be assembled into a more comprehensive towed array.
U.S. Pat. No. 4,222,114 to Rolleigh et al.;
U.S. Pat. No. 4,271,490 to Minohara et al.;
U.S. Pat. No. 4,766,575 to Erlich et al.;
U.S. Pat. No. 4,866,682 to Uchihashi et al.; and
U.S. Pat. No. 6,255,761 to Benjamin.
Specifically, Rolleigh et al. disclose a cylinder array radiator that reduces the intensity of energy radiated in undesirable directions. The radiator is constructed so that vertical staves placed on the face of a cylinder are staggered in the vertical direction by a predetermined distance to cancel energy in the undesirable directions.
The patent to Minohara et al. discloses an ultrasonic detection system having an array of ultrasonic transducers that are uniformly closely disposed relative to each other such that the active surfaces for transmission or reception are maintained on a straight or curved line. The transducers form radiation or reception beams in a specific direction. Beam orientation is accomplished by selecting a group of transducers from the array and/or respectively applying appropriate phase-shifts to the signals to be fed to each of the transducers, or to the signals produced from each of the transducers. Shields are maintained between two adjacent transducers for suppression of sidelobes.
Ehrlich et al. disclose a cylindrical array employing rectangular planar array segments which extend in the axial direction when assembled on a cylindrical conducting plate having flat longitudinal portions to which the planar array segments are attached. Each planar array segment comprises two columns of planar transducer elements with each column extending in the axial direction of the cylinder. The acoustic center of each transducer lies on the circumference of a right circular cylinder. The acoustical requirements of a cylindrical array are satisfied to allow multiple beams to be formed with a minimum of complexity and with the same versatility as in the curved array segment cylindrical array embodiment.
Uchihashi et al. disclose an ultrasonic device comprising a plurality of transducer elements arranged in rows and columns and acoustic insulation material maintained between each two adjacent rows of transducer elements. The ultrasonic device comprises (i) a plurality of rows of the transducer elements, each row being disposed on an imaginary circle, (ii) a plurality of circular plates each supporting one of said rows, and (iii) spacers for spacing adjacent plates of the plurality of plates at a predetermined space interval, thereby forming a cylindrical array.
The patent to Benjamin discloses a piezoelectric composite transducer and method for making the same. A block of piezoelectric material has a common base and a plurality of uniform-length rods extending from the common base in a parallel spaced-apart fashion to define an array. A first surface region is defined at outboard ends of the rods and a side region is defined about the periphery of the array. Electric conductors extend through the side region, are routed parallel to the first surface region, and are then led substantially parallel to the rods to the first surface region. Spaces between the rods are filled up to the first surface region with a visoelastic material. The common base of the block is then removed such that a second surface region parallel and opposite the first surface region is defined. Electrodes are deposited at the first surface region to be in contact with the rods and in electrical contact with the electric conductors. A ground electrode is deposited at the second surface region to be in contact with the rods. The resulting piezoelectric composite transducer can be heated and shaped to conform to complex curves.
It should be understood that the present invention would in fact enhance the functionality of the above patents by providing a modular sub-array for use with a plurality of other modular sub-arrays. It includes a multi-chamber support structure with an acoustically absorptive hub as a basis for the sub-array.